This invention relates to a combined Throttle and Motor control system for use with an AC induction motor connected to a multi-speed transmission, either manual or automatic.
In my earlier US patent application Serial No.09/676,775, filed Oct. 2 2000 and entitled xe2x80x9cAC Motor Control for a Vehicle having a multi-speed Transmission 11xe2x80x9d the problems of ac motor control throughout shifts of a multi-speed transmission were essentially solved. In essence smooth transmission shifts were made based on a constant vehicle speed throughout the shifts. Prior to up-shifting the motor was rotating at a certain selected rpm. Following the shift the motor rotated at a selected lower rpm based on a change in the overall transmission ratio. During the shifting all operative power was removed. The power to the motor was only reapplied when the new reduced motor rpm was appropriate for the degree of change in the overall transmission ratio. Conversely, downshifting caused an increase in motor rpm but was handled in a manner similar to up-shifting. The small momentum of the rotor was no match for the vehicle momentum when the clutch was engaged, hence the motor rapidly adjusted to the new rpm following re-engagement of the clutch. The gear ratio following the shift was automatically identified by dividing the smaller wheel rpm into the larger motor rpm and comparing its value with known overall speed reduction ratios. When two successive control cycle checks indicated the same valid transmission ratio, within reasonable limits, the shift was considered to be complete and power was restored.
The changes in the motor rpm was correctly accounted for throughout the shifts by reducing the motor rpm to its new changed rpm following a shift. Since the change required is quite large, especially in the lower gears, this prevented stalling on up-shifting and large regenerative currents on downshifting.
Unfortunately, however, throttle control is also affected by the gear change. Assuming a shift from 1st gear to 2nd gear. A typical change in motor rpm following the up-shift is 45%. Following the shift the motor will be correctly re-powered at its new rpm but the throttle remains in the same position as previously and since the throttle is used directly to control motor rpm it has essentially lost control.
Thus, it is an object of the present invention to provide a motor control system which combines the earlier results of motor control throughout transmission shifts with a throttle control technique for maintaining constant throttle control throughout the shifts. A novel and easily implemented solution is available for systems which use a finite set of fixed speeds. Other solutions for addressing this problem have not been found.
Since the solution is limited to a finite set of discrete speeds, a Patel and Hoft harmonic reduced set of discrete speeds as described in xe2x80x9cGeneralized Techniques of Harmonic Elimination and Voltage Control in Thyristor Invertersxe2x80x9d, Part I, Harmonic Elimination, IEEE Trans. on Industrial Applications, Vol 1 A-9, No 3, May-June 1973, pp 310-317, Patel and Hoft, is recommended. The Patel and Hoft generated speeds have their five most troublesome harmonics nearly completely eliminated. This permits motor and inverter design to use only passive cooling instead of the liquid cooling of most current implementations. When generating the discrete speeds a minimal separation between the speed members is desirable for use with a multi-speed transmission.
An electronic controller for setting the speed of an AC motor, when limited to a set of discrete speeds, is programmed to include a table of ascending speeds starting with zero rpm up to a selected maximum desired rpm. The controller then measures the motor""s rotor speed. The discrete rpm immediately higher than this speed in the table is selected as the current motor rpm. The one immediately higher than that in the table is selected as an acceleration rpm. The one of lower speed than the current rpm is selected as a deceleration rpm. A linear throttle control may be used to access any members of the speed table. For any throttle position which maps into a position in the speed table equal or higher than the acceleration rpm an acceleration is called for. If the throttle is also used to control deceleration then any throttle position which maps equal or below the deceleration rpm in the table may be used for throttle control of deceleration. Optionally, for deceleration, the vehicle""s brake lamp signal may be used to activate the motor at the current deceleration rpm from the table.
The spacing between the discrete speeds in the speed table provides a means for controlling acceleration. Large spacings typically increase acceleration but result in larger motor slips, rougher control and lower efficiency. A compromise amongst the various options may, therefore, be desirable.
This invention is suited for use in an electric vehicle or any other system that uses a DC power source and a digitally controlled inverter to drive an AC induction motor. The digital control system provides a discrete series of motor speeds by reference to pre-established sets of instructions for generating waveforms, there being instructions for generating waveforms at a number of discrete frequencies.
Thus, by one aspect of this invention there is provided a throttle control system for use throughout gear shifts in an AC motor and multi-speed transmission system, comprising:
a) removing power from said motor prior to a gear shift;
b) selecting an acceptable after-shift motor speed at a selected pre-shift throttle position, from a set of master tables of harmonically reduced computer generated motor speeds for each gear ratio in said multi speed transmission;
c) adjusting motor speed to said acceptable afterxe2x80x94shift motor speed; and
d) reapplying power to said motor.